RJ11 For Modems And Telephony
RJ11 connection cable
The RJ45 network connector and the RJ11 look superficially alike, but the RJ11 has only four leads (or contacts) whereas the RJ45 has eight. In computer systems, the RJ11 is used primarily for connecting to modems. There are many different adapters for RJ11 connectors, because telephone ports vary widely from country to country.
RJ11 ports on a notebook PC
RJ11 modem connector
RJ11 adapters convert between regional telecomm variations, this one works for Germany. In the long term country-specific versions are on the wane.